drm/amdgpu: validate doorbell_offset in user queue creation

amdgpu_userq_get_doorbell_index() passes the user-provided
doorbell_offset to amdgpu_doorbell_index_on_bar() without bounds
checking. An arbitrarily large doorbell_offset can cause the
calculated doorbell index to fall outside the allocated doorbell BO,
potentially corrupting kernel doorbell space.

Validate that doorbell_offset falls within the doorbell BO before
computing the BAR index, using u64 arithmetic to prevent overflow.

Fixes: f09c1e6 ("drm/amdgpu: generate doorbell index for userqueue")
Reported-by: Yuhao Jiang <[email protected]>
Signed-off-by: Junrui Luo <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
(cherry picked from commit de1ef4f)
Cc: [email protected]

Author: avasummer

drivers/gpu/drm/amd/amdgpu/amdgpu_userq.c

@@ -600,6 +600,13 @@ amdgpu_userq_get_doorbell_index(struct amdgpu_userq_mgr *uq_mgr,
 		goto unpin_bo;
 	}
 
+	/* Validate doorbell_offset is within the doorbell BO */
+	if ((u64)db_info->doorbell_offset * db_size + db_size >
+	    amdgpu_bo_size(db_obj->obj)) {
+		r = -EINVAL;
+		goto unpin_bo;
+	}
+
 	index = amdgpu_doorbell_index_on_bar(uq_mgr->adev, db_obj->obj,
 					     db_info->doorbell_offset, db_size);
 	drm_dbg_driver(adev_to_drm(uq_mgr->adev),